Hello, here's my guide to Annie! I build her as a tanky caster with a HUGE burst. Summon: Tibbers will make every ad carry cry and force them to buy things like banshees veil. Annie has great scaling throughout the game and can be a game-changing addition to any team. With her passive ability, she can stun with ease, from one target to multiple enemies. Without further ado, let's unveil my version of annie!

Pros:

Huge burst
AOE stun
a bit tanky
troll bear

Cons:

Hard to start off early game
Squishy until catalyst
Mana starved if continually harassing

I build a pretty standard rune page for Annie. Magic penetration reds are staple for ap casters. I get health per level seals because I want Annie to be extra tanky when bursting. Ability per level blues are standard to maximize damage potential. And finally, flat ability power quints are a must for early damage.

There's nothing unusual about these runes but feel free to comment if there's a better option for you guys!

Pyromania (Innate): After every 4 spell casts, Annie's next offensive spell will stun its target for 1.75 seconds.

This is the game changing passive I was talking about earlier. Using this effectively is what separates good annie players from great ones. It's a good idea to save the stun during a team fight. Due to the recent patch, Annie's Molten Shield cooldown decreased significantly so I would use that when I have 3 charges of my passive so my enemies' don't see that circle thing around Annie. Being able to pull this out at a moment's notice can really save you or secure you the kill.

Disintegrate (Active): Annie shoots a mana infused fireball, dealing magic damage to her target. The mana cost is refunded if it kills the target.
Cooldown: 4 seconds
Range: 625
Cost: 60 / 70 / 80 / 90 / 100 mana
Magic Damage: 85 / 125 / 165 / 205 / 245 (+0.7 per ability power)

This will be your main ability you're gonna use throughout the laning phase. It refunds you mana if you successfully kill something with it so use if for last hitting minions. Don't be afraid to use it even if you have the stun charged up because chances are you won't be needing it unless it's pretty far into the early game or if you can harass the enemy champ right away. The standard harass combo would be a Disintegrate into an Incinerate. Speaking of which...

Incinerate (Active): Annie casts a cone of fire in front of her, dealing magic damage to all enemies in the area.
Cooldown: 8 seconds.
Range: 625
Cone Width: ~45º
Cost: 70 / 80 / 90 / 100 / 110 mana
Magic Damage: 80 / 130 / 180 / 230 / 280 (+0.75 per ability power)

This will be the second main source of damage after Disintegrate. This spell has huge scaling (0.75 AP) but we only max it second because Disintegrate is more reliable as a damage source and as a farming tool. However, don't underestimate this skill, it does tons of AOE damage.

Molten Shield (Active): Places a shield around Annie for 8 seconds that increases her armor and magic resistance. Additionally, enemies will be dealt magic damage whenever they use auto-attacks on her while the shield is active.
Cost: 20 mana
Cooldown: 16 seconds
Armor & Magic Resistance: 20 / 30 / 40 / 50 / 60
Magic Damage: 20 / 30 / 40 / 50 / 60 (+0.2 per ability power)

This was the skill I was talking about earlier when I said to use it for charging up the stun passive. The armor/magic resist is great as a bonus but the real value is it's for adding an addition spell to the pyromania charge. It requires quick thinking but it can give you a stun in basically one shot if you have three charges. The damage is pretty significant as well, acting like a Thornmail. Always turn it on in a team fight, remember your also tanky as well as a damage dealer.

Summon: Tibbers (Active): Annie releases her bear Tibbers from his toy prison, dealing magic damage to enemy units in the summon area. For a limited time of 45 seconds, Tibbers can move and attack at Annie's will, while continually dealing magic damage to surrounding enemies.
Cooldown: 120 seconds.
Range to center of Summon's AoE: 600 (estimate)
Radius of Summon's AoE: 150
Radius of Tibbers' Aura AoE: 200
Continual Magic Damage: 35 (+0.2 per ability power)
Cost: 125 / 175 / 225 mana
Summon Magic Damage: 200 / 325 / 450 (+0.7 per ability power)

Tibbers' Attack Damage: 85 / 105 / 130

Tibbers' Health: 1200 / 1600 / 2000

Tibbers' Armor: 30 / 50 / 70

Tibbers' Magic Resist: 25 / 45 / 65

This is the spell that makes enemy champs go "WTF ANNIE OP GTFO OF HERE". This is the main spell you will use when you're trying to put that AOE stun on everyone. It does huge initial magic damage and it does significant damage over time damage if left unchecked. Tibbers also has decent health and damage, as well as an aura that deal constant magic damage around him. You can micro him with alt+right cick. It's pretty hard but doing so might land you an extra kill or turret fodder.

Info taken from http://leagueoflegends.wikia.com/wiki/Annie_the_Dark_Child

I mentioned this before but I'll reiterate again. Disintegrate is leveled up first because it is the better and more reliable damage skill that also serves as a great last hitting tool. It refunds mana when it kills a unit so it makes last hitting a breeze. Incinerate is maxed second as the second damage dealing spell. It provides nice damage and is a huge part of Annie's burst damage. Molten Shield is maxed last because it's primary use is the additional spell for the pyromania charge. However, don't underestimate the armor/magic resist bonus. 60 is a huge amount and it's basically free! Besides, Annie will have alot of health because of her Rod of Ages so the extra protection will be more noticable in a team fight late game.

The first item you will get is Boots and 3 health pots. This is the standard for all AP caster mid because it offers the extra mobility and sustainability in lane. Mobility is necessary to dodge potential skill shots and it makes you a bit faster to put out your own damage. It's better than, let's say, doran's ring because Annie doesn't really need mana regen because she can last hit minions with her spells for free. The extra ability power from doran's ring is nice, but so is the ability power from our runes. Try to finish the boots into sorcerer shoes immediately for the extra magic pen and movement.

Our first major purchase is Rod of Ages. This is the single item that labels Annie as a tanky caster. Annie becomes significantly more tanky with this item because it grants a stupid amount of health as it charges. It make's you live longer to put that extra Disintegrate or Incinerate in in a team fight. The item component Catalyst of Aeons is what feeds you HP and mana early game. Without it, Annie would die before she could put down a single spell. Summon: Tibbers has a pretty short range if you think about it so maximizing it's use would require you to put yourself closer to the enemy. Rod of Ages is a must for Annie.

The next purchase is Rabadon's Deathcap This will greatly increase your AP. Pretty standard for AP casters. The next item is Zhonya's Hourglass This item is critical for [annie] because it offers a 2 second invulnerability. Annie's cooldown on Disintegrate is roughly ~2.4 seconds at max cooldown reduction. 2 seconds of invulnerability guarantees you an extra Disintegrate when you come out of it. Plus it gives more AP and armor, always nice for the tanky caster.

The fifth item in the sequence is lichbane. Annie doesn't really have anything to do when she finished her combo. For the most part, I just autoattack my target after my combo if the champ isn't dead yet. lichbane offers a heck more damage because it adds ALL of you ability power as attack damage in your next basic attack. It also complements Annie's short cooldown on her Disintegrate and it offers movement speed and magic resist, critical when you reach late game as a tanky caster.

The final item is Void Staff. By the time you reach this far in the game, your opponents will realize what a threat you are and they will buy magic resist to compensate. A safe buy is the Void Staff because it offers even more ability power but also gives a 40% magic penetration. The effectiveness of this is usually better than flat magic penetration after the 120 magic resistance mark. Use your judgment when purchasing the last item. Good substitutes can be Banshee's Veil or rylai's crysta scepter.

Don't forget to buy your elixer of fortitude and brilliance when you have too much money! And never forget to ward -.-

Annie is a great champ that can pull together a huge stun and carry games all around. She's really easy to pick up and she's definitely worth the 450ip. She can be hard to master and many people don't recognize her as a "skill" champ but she definitely requires skill to be effective. Annie brings great damage and pressure for the team and I hope you can enjoy playing her!

Please comment/vote to let me know how this guide worked for you (: